U.S. patent number 11,063,558 [Application Number 16/114,708] was granted by the patent office on 2021-07-13 for direct-current tuning of bulk acoustic wave resonator devices.
This patent grant is currently assigned to TEXAS INSTRUMENTS INCORPORATED. The grantee listed for this patent is TEXAS INSTRUMENTS INCORPORATED. Invention is credited to Bichoy Bahr, Baher Haroun, Ali Kiaei, Ting-Ta Yen.
United States Patent |
11,063,558 |
Bahr , et al. |
July 13, 2021 |
Direct-current tuning of bulk acoustic wave resonator devices
Abstract
A system includes a tunable bulk acoustic wave (BAW) resonator
device and a direct-current (DC) tuning controller coupled to the
tunable BAW resonator device. The system also includes an
oscillator circuit coupled to the tunable BAW resonator device. The
DC tuning controller selectively adjusts a DC tuning signal applied
to the tunable BAW resonator device to adjust a signal frequency
generated by the oscillator circuit.
Inventors: |
Bahr; Bichoy (Allen, TX),
Haroun; Baher (Allen, TX), Yen; Ting-Ta (San Jose,
CA), Kiaei; Ali (San Jose, CA) |
Applicant: |
Name |
City |
State |
Country |
Type |
TEXAS INSTRUMENTS INCORPORATED |
Dallas |
TX |
US |
|
|
Assignee: |
TEXAS INSTRUMENTS INCORPORATED
(Dallas, TX)
|
Family
ID: |
1000005675123 |
Appl.
No.: |
16/114,708 |
Filed: |
August 28, 2018 |
Prior Publication Data
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|
|
Document
Identifier |
Publication Date |
|
US 20200076366 A1 |
Mar 5, 2020 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L
41/047 (20130101); H03H 9/205 (20130101); H01L
41/0805 (20130101); H03H 9/17 (20130101); H03B
5/326 (20130101); H03B 2200/0022 (20130101); H03H
2009/02196 (20130101) |
Current International
Class: |
H03B
5/32 (20060101); H01L 41/08 (20060101); H03H
9/17 (20060101); H01L 41/047 (20060101); H03H
9/02 (20060101); H03H 9/205 (20060101) |
Field of
Search: |
;333/187,188
;331/107A,116R,154,162,163,177R,185,48 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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11-168345 |
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Jun 1999 |
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JP |
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2010-093398 |
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Apr 2010 |
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JP |
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Other References
C Enz, et al., "Ultra Low-Power MEMS-based Radio for Wireless
Sensor Networks," Circuit Theory and Design, European Conference
on, 2007, ECCTD 2007. pp. 320-331. cited by applicant .
C. Enz, et al., "Building Blocks for an Ultra Low-Power MEMS-based
Radio." IEEEE International Workshop on Radio-Frequency Integration
Technology, Dec. 9-11, 2007, Singapore. pp. 158-167. cited by
applicant .
David Ruffieux, "A High-Stability, Ultra-Low-Power Differential
Oscillator Circuit for Demanding Radio Applications," ESSCIRC 2002.
pp. 85-88. cited by applicant .
Y. Chang et al, "A Differential Digitally Controlled Crystal
Oscillator With a 14-Bit Tuning Resolution and Sine Wave Outputs
for Cellular Applications," IEEE JSSC (vol. 47, No. 2, pp. 421-434,
Feb. 2012). cited by applicant.
|
Primary Examiner: Summons; Barbara
Attorney, Agent or Firm: Davis. , Jr.; Michael A. Brill;
Charles A. Cimino; Frank D.
Claims
What is claimed is:
1. A system comprising: a bulk acoustic wave (BAW) resonator
including: a first electrode; separate first and second
piezoelectric layers with respective first sides contacting the
first electrode; a second electrode contacting a second side of the
first piezoelectric layer; and a third electrode contacting a
second side of the second piezoelectric layer, in which the third
electrode is separate from the second electrode; an oscillator
circuit coupled to the BAW resonator, the oscillator circuit
configured to generate an oscillating signal having a frequency;
and a direct-current (DC) controller coupled to the BAW resonator,
the DC controller configured to adjust the frequency by adjusting a
DC signal to the BAW resonator.
2. The system of claim 1, wherein the BAW resonator comprises a
single three-electrode BAW resonator core.
3. The system of claim 1, wherein the DC controller is configured
to adjust the DC signal based on at least one of a temperature
measurement and a stress measurement.
4. The system of claim 1, wherein the DC controller is configured
to adjust the DC signal based on at least one of a measured
frequency drift and an estimated frequency drift.
5. A system comprising: a bulk acoustic wave (BAW) resonator
including a single two-electrode BAW resonator core with a first
electrode and a second electrode; an oscillator circuit having
first and second terminals, the oscillator circuit coupled to the
BAW resonator, and the oscillator circuit configured to generate an
oscillating signal having a frequency, in which the first and
second electrodes are DC isolated from the first and second
terminals; and a direct-current (DC) controller coupled to the BAW
resonator, the DC controller configured to adjust the frequency by
adjusting a DC signal to the BAW resonator; a first resistor
between a DC terminal of the BAW resonator and one of the first and
second electrodes; and a second resistor between a ground node and
the other of the first and second electrodes.
6. A system comprising: a bulk acoustic wave (BAW) resonator
including a pair of two-electrode BAW resonator cores in different
integrated circuits; an oscillator circuit coupled to the BAW
resonator, the oscillator circuit configured to generate an
oscillating signal having a frequency; and a direct-current (DC)
controller coupled to the BAW resonator, the DC controller
configured to adjust the frequency by adjusting a DC signal to the
BAW resonator.
7. A method comprising: adjusting, by a direct-current (DC)
controller, a DC signal to a bulk-acoustic wave (BAW) resonator to
adjust a signal frequency of an oscillator circuit, wherein the BAW
resonator includes: a first electrode; separate first and second
piezoelectric layers with respective first sides contacting the
first electrode; a second electrode contacting a second side of the
first piezoelectric layer; and a third electrode contacting a
second side of the second piezoelectric layer, in which the third
electrode is separate from the second electrode.
8. The method of claim 7, wherein the BAW resonator comprises a
single three-electrode BAW resonator core, and the method further
comprises coupling the single three-electrode BAW resonator core to
the DC controller and the oscillator circuit via isolated
terminals.
9. The method of claim 7, further comprising: receiving, by the DC
controller, an ambient measurement; and adjusting the DC signal to
the BAW resonator based on the ambient measurement.
10. The method of claim 7, further comprising: receiving, by the DC
controller, a drift frequency measurement or estimate; and
adjusting the DC signal to the BAW resonator based on the drift
frequency measurement or estimate.
11. A method comprising: adjusting, by a direct-current (DC)
controller, a DC signal to a bulk-acoustic wave (BAW) resonator to
adjust a signal frequency of an oscillator circuit, wherein the BAW
resonator includes a single two-electrode BAW resonator core with a
first electrode and a second electrode; coupling the single
two-electrode BAW resonator core to the DC controller and the
oscillator circuit via isolated terminals; coupling a first
resistor between a DC terminal of the BAW resonator corresponding
to one of the first and second electrodes; and coupling a second
resistor between a ground node and the other of the first and
second electrodes.
12. A BAW resonator device comprising: a BAW resonator core
including: a first electrode; a second electrode; a third
electrode, in which the third electrode is separate from the second
electrode; and separate first and second layers of electro-active
material having a physical characteristic that changes in response
to a direct-current (DC) signal, wherein respective first sides of
the first and second layers of electro-active material contact the
first electrode, a second side of the first layer of electro-active
material contacts the second electrode, and a second side of the
second layer of electro-active material contacts the third
electrode; a first oscillator terminal coupled to the second
electrode; a second oscillator terminal coupled to the third
electrode; and a direct current (DC) terminal coupled to the first
electrode and configured to receive the DC signal to adjust a
center frequency of the BAW resonator device.
13. The BAW resonator device of claim 12, wherein the BAW resonator
core comprises a three-electrode BAW resonator core having the
first, second, and third electrodes.
14. The BAW resonator device of claim 12, wherein the BAW resonator
core, the first oscillator terminal, the second oscillator
terminal, and the DC terminal are formed in a single integrated
circuit.
15. A BAW resonator device comprising: a BAW resonator core
including: a first electrode; a second electrode; and an
electro-active material having a physical characteristic that
changes in response to a direct-current (DC) signal; a first
oscillator terminal coupled to the first electrode; a second
oscillator terminal coupled to the second electrode; and a direct
current (DC) terminal coupled to one of the first and second
electrodes or the electro-active material and configured to receive
the DC signal to adjust a center frequency of the BAW resonator
device; wherein the BAW resonator core includes a first
two-electrode BAW resonator core and a second two-electrode BAW
resonator core in different integrated circuits, the first
electrode coupled to the first oscillator terminal corresponds to a
first electrode of the first two-electrode BAW resonator core, the
second electrode coupled to the second oscillator terminal
corresponds to a first electrode of the second two-electrode BAW
resonator core, and a second electrode of the first two-electrode
BAW resonator core and a second electrode of the second
two-electrode BAW resonator core are coupled to the DC
terminal.
16. A BAW resonator device comprising: a BAW resonator core
including: a first electrode; a second electrode; and an
electro-active material having a physical characteristic that
changes in response to a direct-current (DC) signal; a first
oscillator terminal coupled to the first electrode; a second
oscillator terminal coupled to the second electrode; a direct
current (DC) terminal coupled to one of the electrodes or the
electro-active material and configured to receive the DC signal to
adjust a center frequency of the BAW resonator device, wherein the
BAW resonator core comprises a two-electrode BAW resonator core
with the first and second electrodes, wherein the first and second
electrodes are DC isolated from the first and second oscillator
terminals; a first resistor between the DC terminal and one of the
first and second electrodes; and a second resistor between a ground
node and the other of the first and second electrodes.
17. The BAW resonator device of claim 16, wherein the first and
second electrodes are DC isolated from the first and second
oscillator terminals by a respective capacitor.
18. A BAW resonator device comprising: a BAW resonator core
including: a first electrode; a second electrode; and an
electro-active material having a physical characteristic that
changes in response to a direct-current (DC) signal; a first
oscillator terminal coupled to the first electrode; a second
oscillator terminal coupled to the second electrode; and a direct
current (DC) terminal coupled to one of the electrodes or the
electro-active material and configured to receive the DC signal to
adjust a center frequency of the BAW resonator device; wherein the
BAW resonator core comprises two BAW resonator cores in different
integrated circuits.
19. A bulk acoustic wave (BAW) resonator device fabrication method
comprising: forming at least one BAW resonator core by: forming a
first electrode; forming first and second piezoelectric layers with
respective first sides contacting the first electrode; forming a
second electrode in contact with a second side of the first
piezoelectric layer; and forming a third electrode in contact with
a second side of the second piezoelectric layer; coupling the
second electrode to a first oscillator terminal; coupling the third
electrode to a second oscillator terminal; and coupling a direct
current (DC) control terminal to the first electrode.
20. The method of claim 19, wherein the BAW resonator core is
formed in a single semiconductor wafer.
Description
BACKGROUND
Timing devices are used as clock sources in a variety of modern
electronic circuits. Such timing devices provide frequency control
and timing for applications ranging from relatively simple crystal
oscillators for mobile phones and radio transmitters to more
complex timing devices for computers and navigational aids.
For portable clock applications, quartz crystal tuned oscillators
(XOs) have good relative frequency accuracy, low frequency drift
(or shift) as a function of temperature, and low noise. However,
while the density of electronics has grown exponentially following
Moore's law, the area and volume occupied by quartz crystals has
not scaled accordingly.
To address the scaling issue for XOs, efforts have been directed
toward replacing the XOs with silicon microelectromechanical
(MEMS)-based resonators (or oscillators) as the frequency source
for clocks. MEMs resonators are effectively time-base generators,
or timing references, similar in operating principle to a
mechanical tuning fork.
Bulk acoustic wave (RAW) resonators use a piezoelectric effect to
convert electrical energy into mechanical energy resulting from an
applied RF voltage and vice versa. A BAW resonator generally
operates at its mechanical resonant frequency, which is defined as
a frequency for which the half wavelength of sound waves
propagating in the device is equal to a total piezoelectric layer
thickness for a given velocity of sound for the material. BAW
resonators operating in the GHz range generally have physical
dimensions of tens of microns in diameter, with thicknesses of a
few microns.
Although BAW resonators offer potential as a frequency reference,
frequency tuning of a BAW resonator has been difficult to address.
One suggested solution involves adding a capacitor across the BAW
resonator, but that solution reduces quality factor and increases
power consumption.
SUMMARY
In a first example, a system comprises a tunable bulk-acoustic wave
(BAW) resonator device and a direct-current (DC) tuning controller
coupled to the tunable BAW resonator device. The system also
comprises an oscillator circuit coupled to the tunable BAW
resonator device. The DC tuning controller selectively adjusts a DC
tuning signal applied to the tunable BAW resonator device to adjust
a signal frequency generated by the oscillator circuit.
In a second example, a method comprises selectively adjusting, by a
direct-current (DC) tuning controller, a DC tuning signal applied
to a tunable bulk-acoustic wave (BAW) resonator device to adjust a
signal frequency of an oscillator circuit.
In a third example, a tunable BAW resonator device comprises a BAW
resonator core. The BAW resonator core comprises a first electrode,
a second electrode, and an electro-active material having a
physical characteristic that changes in response to a DC tuning
signal. The tunable BAW resonator device also comprises a first
oscillator terminal coupled to the first electrode, and a second
oscillator terminal coupled to the second electrode. The tunable
BAW resonator device also comprises a DC tuning terminal, coupled
to one of the electrodes or the electro-active material, to receive
a DC tuning signal to adjust a center frequency of the tunable BAW
resonator device.
In a fourth example, a tunable BAW resonator fabrication method
comprises forming a first two-electrode BAW resonator core and
forming a second two-electrode BAW resonator core. The method also
comprises coupling a first electrode of the first two-electrode BAW
resonator core to a first oscillator terminal, and coupling a first
electrode of the second two-electrode BAW resonator core to a
second oscillator terminal. The method also comprises coupling a
direct current (DC) tuning terminal to respective second electrodes
of the first and second two-electrode BAW resonator cores.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1A-1D show tunable bulk acoustic wave (BAW) resonator devices
in accordance with various examples.
FIGS. 2A-2E show systems with tunable BAW resonator devices in
accordance with various examples.
FIGS. 3A-3C are schematic diagrams of tunable BAW resonator devices
coupled to oscillator circuitry in accordance with various
examples.
FIG. 4 is a cross-sectional view of a three-electrode BAW resonator
core in accordance with various examples.
FIG. 5 is a cross-sectional view of a pair of two-electrode BAW
resonator cores in accordance with various examples.
FIGS. 6A-6C are block diagrams of BAW resonator cores and related
terminals in accordance with various examples.
FIG. 7 is a graph representing BAW resonator frequency shift as a
function of a direct current (DC) tuning voltage in accordance with
various examples.
FIG. 8 is a graph representing BAW resonator quality factor as a
function of a DC tuning voltage in accordance with various
examples.
FIG. 9 is a flowchart of a tunable BAW resonator device fabrication
method in accordance with various examples.
FIG. 10 is a flowchart of another tunable BAW resonator device
fabrication method in accordance with various examples.
FIG. 11 is a flowchart of another tunable BAW resonator device
fabrication method in accordance with various examples.
FIG. 12 is a flowchart of a method involving a tunable BAW
resonator device in accordance with various examples.
DETAILED DESCRIPTION
The examples described herein are directed to tunable bulk-acoustic
wave (BAW) resonator devices and related systems, methods, and
options. Without limitation, some tunable BAW resonator devices
described herein have three terminals, where two of the terminals
are oscillator terminals and the third terminal is a DC turning
terminal. More specifically, the oscillator terminals of a tunable
BAW resonator device are intended to be coupled to an oscillator
circuit. Meanwhile, the DC turning terminal of a tunable BAW
resonator device is intended to be coupled to a DC tuning
controller. In some examples, the oscillator terminals and the DC
tuning terminal of a tunable BAW resonator device are pins or pads
of an integrated circuit or printed circuit board (PCB). In other
examples, the oscillator terminals and DC tuning terminal of a
tunable BAW resonator device are connection points in a circuit.
For example, the oscillator terminals are connection points in a
circuit where a tunable BAW resonator device is coupled to an
oscillator circuit, and the DC tuning terminal is a connection
point in a circuit where a tunable BAW resonator device is coupled
to a DC tuning controller. For at least some tunable BAW resonator
devices, the oscillator terminals are isolated from the DC tuning
terminal.
When adjustments to the center frequency of a tunable BAW resonator
device are desired (e.g., based on measurements and/or
predetermined estimates related to frequency drift), a DC tuning
controller generates and provides a DC tuning signal to the DC
tuning terminal of a tunable BAW resonator device. The DC tuning
signal causes electro-active material (e.g., piezoelectric
materials and/or dielectric materials) of a tunable BAW resonator
device to change a physical characteristic (e.g., size, internal
stress/strain, and/or shape) of such material, resulting in a
shifted center frequency for the tunable BAW resonator device. In
some examples, tuning operations are performed once or periodically
to adjust the signal frequency of an oscillator coupled to a
tunable BAW resonator device. Such tuning is performed in response
to default frequency errors and/or frequency drift due to various
environmental/operational conditions, such as temperature,
humidity, pressure, stress, aging, etc.).
Various tunable BAW resonator devices are possible. In different
examples, a tunable BAW resonator device is made using a single
two-electrode BAW resonator core, a pair of two-electrode BAW
resonator cores, or a three-electrode BAW resonator core. Also, in
different examples, a tunable BAW resonator device is formed in a
single integrated circuit (IC), such as a semiconductor die with
packaging. In other examples, a tunable BAW resonator device is
formed in multiple ICs (e.g., at least two semiconductors dies
packaged together or separately). Also, in different examples, a
tunable BAW resonator device is part of a larger system, such as an
oscillator, a clock, or any semiconductor device that includes an
oscillator or clock (e.g., processors, transmitters, receivers,
peripheral or network interfaces, radar components). In different
examples, each larger system is implemented in a single IC (e.g.,
one semiconductor die with packaging) or multiple ICs (e.g., at
least two semiconductors dies packaged together or separately).
Various tunable BAW resonator device options, scenarios, and
details are described below in reference to the drawings.
FIGS. 1A-1D show tunable BAW resonator devices in accordance with
various examples. In FIG. 1A, a tunable BAW resonator device 100
with a single two-electrode BAW resonator core 102, a first
oscillator terminal 103 (to receive a differential signal, V+), a
second oscillator terminal 105 (to receive a differential signal,
V-), and a DC tuning terminal 107 (to receive a DC tuning signal,
Vtune) is represented. For the tunable BAW resonator device 100,
the first oscillator terminal 103 is coupled to a first electrode
112 of the two-electrode BAW resonator core 102 via isolation
component(s) 104 that block DC voltage from flowing between the
first electrode 112 and the first oscillator terminal 103. Also,
the second oscillator terminal 105 is coupled to a second electrode
114 of the two-electrode BAW resonator core 102 via isolation
component(s) 106 that block DC voltage from flowing between the
second electrode 114 and the second oscillator terminal 105. In
various examples, the isolation component(s) 104 and 106 are
capacitors. Further, the DC tuning terminal 107 is coupled to a
connection point 116 between first electrode 112 and isolation
component(s) 104 via a first resistor 108 to bias the voltage of
Vtune received at the first electrode 112. Also, the second
electrode 114 is coupled to ground via a second resistor 109
connected at a connection point 118 between the second electrode
114 and isolation component(s) 106. In different examples, the
tunable BAW resonator device 100 represents a single IC, multiple
ICs, and/or discrete components on a printed circuit board (PCB).
Also, the terminals 103, 105, and 107 represent pins or pads of an
IC, packaged chip, or PCB.
In an example operation, the first and second oscillator terminals
103 and 105 receive differential alternating current (AC) voltage
signals (V+ and V-) that pass through the isolation component(s)
104 and 106 to the first and second electrodes 112 and 114 of the
two-electrode BAW resonator core 102, resulting in default BAW
resonator behavior (a series resonance at a specific frequency
characterized by a minimal impedance, followed by a parallel
resonance at a specific and higher frequency characterized by a
high impedance between the electrodes 112 and 114 of the BAW
resonator core 102). By selectively adjusting Vtune (applied at the
DC tuning terminal 107), the center frequency of the tunable BAW
resonator 100 is adjusted without passing Vtune to oscillator
circuitry coupled to the first and second oscillator terminals 103
and 105. In one example, adjusting Vtune between 0-10V is
sufficient to account for default frequency errors and/or frequency
drift.
In FIG. 1B, a tunable BAW resonator device 120 with a pair of
two-electrode BAW resonator cores 122 and 124, a first oscillator
terminal 123 (to receive a differential AC signal, V+), a second
oscillator terminal 125 (to receive a differential AC signal, V-),
and a DC tuning terminal 127 (to receive a DC tuning signal, Vtune)
is represented. For the tunable BAW resonator device 120, the first
oscillator terminal 123 is coupled to a first electrode 132 of the
two-electrode BAW resonator core 122. Meanwhile, the second
oscillator terminal 125 is coupled to a first electrode 138 of the
two-electrode BAW resonator core 124. The DC tuning terminal 127 is
coupled to a second electrode 134 of the two-electrode BAW
resonator core 122 and to a second electrode 136 of the
two-electrode BAW resonator core 124. In FIG. 1B, the two-electrode
BAW resonator core 122 is part of a first unit 126, while the
two-electrode BAW resonator core 124 is part of a second unit 128.
In different examples, the units 126 and 128 represent ICs,
packaged chips, or PCBs. Also, the terminals 123, 125, and 127
represent pins or pads of an IC, packaged chip, or PCB.
In an example operation, the first and second oscillator terminals
123 and 125 receive differential AC voltage signals (V+ and V-) and
pass the signals to a respective electrode. More specifically, V+
is received by the first electrode 132 of the two-electrode BAW
resonator core 122, and V- is received by the first electrode 138
of the two-electrode BAW resonator core 124, resulting in default
BAW resonator behavior (a series resonance at a specific frequency
characterized by a minimal impedance, followed by a parallel
resonance at a specific and higher frequency characterized by a
high impedance between the electrodes 132 and 138 of the BAW
resonator cores 122 and 124). In various examples, the
two-electrode BAW resonator cores 122 and 124 are selected to
having matching center frequencies. In one example, the
two-electrode BAW resonator cores 122 and 124 are selected from the
same semiconductor wafer and/or wafer section (e.g., adjacent or
within a threshold distance to each other) to facilitate selection
of BAW resonator cores with matching center frequencies. In another
example, the two-electrode BAW resonator cores 122 and 124 are
selected by testing their center frequencies and pairing BAW
resonator cores whose center frequencies match to within a
threshold tolerance. By selectively adjusting Vtune (applied at the
DC tuning terminal 127), the center frequency of the tunable BAW
resonator device 120 (each of the two-electrode BAW resonator cores
122 and 124 is affected) is adjusted. In one example, adjusting
Vtune between 0-10V is sufficient to account for default frequency
errors and/or frequency drift.
In FIG. 1C, a tunable BAW resonator device 140 with a pair of
two-electrode BAW resonator cores 142 and 144, a first oscillator
terminal 143 (to receive a differential AC signal, V+), a second
oscillator terminal 145 (to receive a differential signal, V-), and
a DC tuning terminal 147 (to receive a DC tuning signal, Vtune) is
represented. For the tunable BAW resonator device 140, the first
oscillator terminal 143 is coupled to a first electrode 152 of the
two-electrode BAW resonator core 142. Meanwhile, the second
oscillator terminal 145 is coupled to a first electrode 158 of the
two-electrode BAW resonator core 144. Also, the DC tuning terminal
147 is coupled to a second electrode 154 of the two-electrode BAW
resonator core 142 and a second electrode 156 of the two-electrode
BAW resonator core 144. In FIG. 1C, the two-electrode BAW resonator
cores 142 and 144 are part of a single unit 146, which represents
an IC, packaged chip, or PCB. Also, the terminals 143, 145, and 147
represent pins or pads of an IC, packaged chip, or PCB.
In an example operation, the first and second oscillator terminals
143 and 145 receive differential AC voltage signals (V+ and V-) and
pass the signals to a respective electrode. More specifically, V+
is received by the first electrode 152 of the two-electrode BAW
resonator core 142, and V- is received by the first electrode 158
of the two-electrode BAW resonator core 144, resulting in default
BAW resonator behavior (a series resonance at a specific frequency
characterized by a minimal impedance, followed by a parallel
resonance at a specific and higher frequency characterized by a
high impedance between the electrodes 152 and 158 of the BAW
resonator cores 142 and 144). In one example, the two-electrode BAW
resonator cores 142 and 144 are selected from the same
semiconductor wafer and/or wafer section (e.g., adjacent or within
a threshold distance to each other) to facilitate selection of BAW
resonator cores with matching center frequencies. In another
example, the two-electrode BAW resonator cores 142 and 144 are
selected by testing their center frequencies and pairing BAW
resonator cores whose center frequencies match to within a
threshold tolerance. By selectively adjusting Vtune (applied at the
DC tuning terminal 147), the center frequency of the tunable BAW
resonator device 140 (each of the two-electrode BAW resonator cores
142 and 144 is affected) is adjusted. In one example, adjusting
Vtune between 0-10V is sufficient to account for default frequency
errors and/or frequency drift.
In FIG. 1D, a tunable BAW resonator device 160 with a single
three-electrode BAW resonator core 162, a first oscillator terminal
163 (to receive a differential signal, V+), a second oscillator
terminal 165 (to receive a differential signal, V-), and a DC
tuning terminal 167 (to receive a DC tuning signal, Vtune) is
represented. For the tunable BAW resonator device 160, the first
oscillator terminal 163 is coupled to a first electrode 172 of the
three-electrode BAW resonator core 162. Meanwhile, the second
oscillator terminal 165 is coupled to a second electrode 174 of the
three-electrode BAW resonator core 162. Finally, the DC tuning
terminal 167 is coupled to a third electrode 176 of the
three-electrode BAW resonator core 162. In FIG. 1D, the
three-electrode BAW resonator core 162 represents an IC. Meanwhile,
the terminals 163, 165, and 167 represent pins or pads of an IC,
packaged chip, or PCB.
In an example operation, the first and second oscillator terminals
163 and 165 receive differential AC voltage signals (V+ and V-) and
pass the signals to a respective electrode. More specifically, V+
is received by the first electrode 172 of the three-electrode BAW
resonator core 162, and V- is received by the second electrode 174
of the three-electrode BAW resonator core 162, resulting in default
BAW resonator behavior (a series resonance at a specific frequency
characterized by a minimal impedance, followed by a parallel
resonance at a specific and higher frequency characterized by a
high impedance between the electrodes 172 and 174 of the
three-electrode BAW resonator core 162). By selectively adjusting
Vtune (applied at the DC tuning terminal 167 and passed to the
third electrode 176 of the three-electrode BAW resonator core 162),
the center frequency of the tunable BAW resonator device 160 is
adjusted. In one example, adjusting Vtune between 0-10V is
sufficient to account for default frequency errors and/or frequency
drift.
FIG. 2A is a block diagram of an oscillator system 200 including a
tunable BAW resonator device 202 (e.g., one of the devices 100,
120, 140, or 160 in FIGS. 1A-1D). In FIG. 2A, the tunable BAW
resonator device 202 has two oscillator terminals 203 and 205
coupled to an oscillator core 208. Meanwhile, a DC tuning terminal
207 of the tunable BAW resonator device 202 is coupled to a
controller 209. In some examples, the controller 209 is separate
from the oscillator system 200 as shown. In other examples, the
controller 209 is included with the oscillator system 200. In
operation, the controller 209 adjusts Vtune based on a temperature
measurement, stress measurement, predetermined frequency drift
values, and/or measured frequency drift values. In various
examples, the controller 209 includes internal components to obtain
temperature measurements, stress measurements, predetermined
frequency drift values, and/or measured frequency drift values. In
other examples, the controller 209 obtains temperature
measurements, stress measurements, predetermined frequency drift
values, and/or measured frequency drift values from external
components (not shown).
In some examples, the oscillator system 200 is a stacked package
(e.g., flip chip assembly) or a lateral package arrangement. In
other examples, the tunable BAW resonator device 202 and oscillator
core 208 are formed in a same integrated circuit die. Also, the
oscillator core 208 has bond pads (not shown) for being coupled
between a high voltage supply terminal (VCC) and a low voltage
shown as a ground, and for being coupled to the oscillator
terminals 203 and 205 of the tunable BAW resonator device 202.
In operation, the tunable BAW resonator device 202 is a very
high-quality (very narrow band) bandpass filter, that together with
the oscillator core 208 functions as a signal generator, generating
sinusoidal or square output waveform at a predetermined and precise
BAW series or parallel resonance frequency. In various examples,
the oscillator core 208 comprises active and passive circuit
elements (e.g., capacitors) capable of sustaining oscillations and
amplifying the signal from the tunable BAW resonator device 202 to
generate and provide the output signal shown as OUT. Construction
features of the tunable BAW resonator device 202 (e.g., the
thickness of its piezoelectric layer(s)) determines the oscillation
frequency. In one example, the oscillator core 208 is a Colpitts
oscillator.
FIG. 2B is a block diagram of a clock system 210 including an
oscillator system 216 (e.g., an example of the oscillator system
200 in FIG. 2A) coupled to a phase-lock-loop (PLL) 222. Similar to
the oscillator system 200 of FIG. 2A, the oscillator system 216 of
FIG. 2B includes a tunable BAW resonator device 212 (e.g., one of
the devices 100, 120, 140, or 160 in FIGS. 1A-1D) with two
oscillator terminals 213 and 215 coupled to an oscillator core 214,
and with a DC tuning terminal 217 coupled to a controller 219. In
at least some examples, the operation of the oscillator system 216
follows the operation of the oscillator system 200 of FIG. 2A, and
the operation of the controller 219 follows the operation of the
controller 209 of FIG. 2A.
The output of the oscillator system 216 (labeled OUT) is processed
by a gain buffer 218, which outputs an amplified and buffered
reference signal 220. The reference signal 222 is divided as
desired and then input to the PLL 222 to generate a desired output
frequency (OUT.sub.PLL), where OUT.sub.PLL is the clock output for
the clock system 210.
FIG. 2C is a block diagram of an IC system 230 including an
oscillator system 234 (e.g., an example of the oscillator system
200 in FIG. 2A) and IC component(s) 236. Similar to the oscillator
system 200 of FIG. 2A, the oscillator system 234 of FIG. 2C
includes a tunable BAW resonator device 232 (e.g., one of the
devices 100, 120, 140, or 160 in FIGS. 1A-1D) with two oscillator
terminals 233 and 235 coupled to an oscillator core (not shown),
and a DC tuning terminal 237 coupled to a controller 239. In at
least some examples, the operation of the oscillator system 234
follows the operation of the oscillator system 200 of FIG. 2A, and
the operation of the controller 239 follows the operation of the
controller 209 of FIG. 2A. In various examples, the IC component(s)
236 include a processor, a transmitter, a receiver, a peripheral or
network interface, and/or a radar component, where the IC
component(s) 236 uses the OUT signal generated by the oscillator
system 234.
FIG. 2D is a block diagram of another IC system 240 including a
clock system 244 (e.g., an example of the clock system 210 in FIG.
2B) and IC component(s) 246. Similar to the clock system 210 of
FIG. 2B, the clock system 244 of FIG. 2D includes a tunable BAW
resonator device 242 (e.g., one of the devices 100, 120, 140, or
160 in FIGS. 1A-1D) with two oscillator terminals 243 and 245
coupled to an oscillator core (not shown), and a DC tuning terminal
247 coupled to a controller 249. In at least some examples, the
operation of the clock system 244 follows the operation of the
Clock system 210 of FIG. 2B, and the operation of the controller
249 follows the operation of the controller 209 of FIG. 2A. In
various examples, the IC component(s) 246 include a processor, a
transmitter, a receiver, a peripheral or network interface, and/or
a radar component, where the IC component(s) 246 uses the
OUT.sub.PLL signal from the clock system 244.
In various other examples, an IC system includes both an oscillator
system and a clock system. In different examples, tunable BAW
resonator devices (e.g., one of the devices 100, 120, 140, or 160
in FIGS. 1A-1D), oscillator systems (e.g., one of the systems 200,
216, or 234 in FIGS. 2A-2C), clock systems (e.g., one of the
systems 210 or 244 in FIGS. 2B and 2D), or IC systems (e.g., one of
the systems 230 or 240 in FIGS. 2C and 2D) are implemented in one
IC (one unpackaged or packaged die) or multiple ICs (multiple
unpackaged or packaged dies). When multiple ICs are used, the ICs
can be packaged together or separately. When packaged separately, a
PCB is used to connect the separate packages.
FIG. 2E shows block diagram of a generic system 250 that employs a
tunable BAW resonator device 252. In different examples, the
tunable BAW resonator device 252 is one of the devices described
above (e.g., one of the devices 100, 120, 140, or 160 in FIGS.
1A-1D). In other examples, the tunable BAW resonator device 252 is
a two-terminal BAW resonator device. In either case, the tunable
BAW resonator device 252 receives a DC tuning voltage (Vtune) from
a DC tuning controller 259 and provides resonator functionality for
system component(s) 256. The system component(s) 256 are oscillator
components (e.g., components used in an oscillator system, such as
oscillator system 200 in FIG. 2A), clock components (e.g.,
components used in a clock system, such as clock system 210 in FIG.
2B), IC components (e.g., components used in an IC system, such as
IC systems 230 and 240 in FIGS. 2C and 2D), and/or other
components. In system 250, the DC tuning controller 259 generates
and provides Vtune to the tunable BAW resonator device 252 in
response to control parameter(s), such as temperature measurements,
stress measurements, predetermined frequency drift values, and/or
measured frequency drift values.
FIGS. 3A-3C show schematic diagrams of tunable BAW resonator
devices coupled to oscillator circuitry in accordance with various
examples. In FIG. 3A, an example oscillator schematic 300 includes
a tunable BAW resonator device 301 that follows the arrangement
given for the tunable BAW resonator device 100 in FIG. 1A. More
specifically, the tunable BAW resonator device 301 has a
two-electrode BAW resonator core 302, capacitors 310 and 312, and
resistors 314 and 316 arranged as shown for the tunable BAW
resonator device 100 in FIG. 1A.
In schematic 300, the first and second oscillator terminals 313 and
315 of the tunable BAW resonator 301 are coupled to respective
transistors (T1 and T2) of an oscillator circuit 320. The
oscillator circuit 320 also includes a capacitor (C1), and
additional transistors (T3 and T4). As desired, T1 and T2 of the
oscillator circuit 320 are biased by current sources 306 and 308 of
a bias circuit 304. In different examples, the components of the
bias circuit 304 (e.g., the component topology for the current
sources 306 and 308), and the components of the oscillator circuit
320 (e.g., the oscillator core topology) may vary.
In FIG. 3B, an example oscillator schematic 330 includes a tunable
BAW resonator device 331 that follows the arrangement given for the
tunable BAW resonator devices 120 and 140 in FIGS. 1B and 1C. More
specifically, the tunable BAW resonator device 331 has a pair of
two-electrode BAW resonator cores 332 and 333 arranged as shown for
the tunable BAW resonator devices 120 and 140 in FIGS. 1B and
1C.
In schematic 330, the first and second oscillator terminals 343 and
345 of the tunable BAW resonator 331 are coupled to respective
transistors (T5 and T6) of an oscillator circuit 350. The
oscillator circuit 350 also includes a capacitor (C2), and
additional transistors (T7 and T8). As desired, T5 and T6 of the
oscillator circuit 350 are biased by current sources 336 and 338 of
a bias circuit 334. In different examples, the components of the
bias circuit 334 (e.g., the component topology for the current
sources 336 and 338), and the components of the oscillator circuit
350 (e.g., the oscillator core topology) may vary.
In FIG. 3C, an example oscillator schematic 360 includes a tunable
BAW resonator device 361 that follows the arrangement given for the
tunable BAW resonator device 160 in FIG. 1D. More specifically, the
tunable BAW resonator device 361 has a single three-electrode BAW
resonator core 362 arranged as shown for the tunable BAW resonator
device 160 in FIG. 1D.
In schematic 360, the first and second oscillator terminals 373 and
375 of the tunable BAW resonator 361 are coupled to respective
transistors (T9 and T10) of an oscillator circuit 380. The
oscillator circuit 380 also includes a capacitor (C3), and
additional transistors (T11 and T12). As desired, T9 and T10 of the
oscillator circuit 380 are biased by current sources 366 and 368 of
a bias circuit 364. In different examples, the components of the
bias circuit 364 (e.g., the component topology for the current
sources 366 and 368), and the components of the oscillator circuit
380 (e.g., the oscillator core topology) may vary.
FIG. 4 shows a cross-sectional view of a three-electrode BAW
resonator core 400 (e.g., the three-electrode BAW resonator core
162 in FIG. 1D) in accordance with various examples. The
three-electrode BAW resonator core 400 in FIG. 4 is an example of a
solidly mounted resonator (SMR) that includes various layers formed
over a semiconductor substrate 401. More specifically, the layers
formed over the semiconductor substrate 401 include electro-active
materials 410 (e.g., Bragg mirrors), a bottom electrode 402,
electro-active materials 406A and 406B (e.g., piezoelectric
materials), insulative layers 412A and 412B, top electrodes 404A
and 404B, and electro-active materials 408A and 408B (e.g., Bragg
mirrors). The three-electrode BAW resonator core 400 also includes
a first metal node 432 coupled to the top electrode 404A, a second
metal node 434 coupled to the other top electrode 404B, and a third
metal node 430 coupled to the bottom electrode 402. In some
examples, the metal node 430 is the DC tuning terminal 167 in FIG.
1D, the metal node 432 is the oscillator terminal 163 in FIG. 1D,
and the metal node 434 is the oscillator terminal 165 in FIG. 1D.
In other examples, the metal nodes 430, 432, 434 are coupled to
external metal terminals (not shown) that facilitate coupling the
three-electrode BAW resonator core 400 to other components (e.g.,
components of an oscillator unit, a clock unit, or an IC unit).
In various examples: the substrate 401 is formed from silicon; the
electro-active materials 410 include layers from different
materials, such as silicon carbide (SiC), methyl silsesquioxane
(MSQ), silicon dioxide (SiO2), silicon carbo hydroxide (SiCOH),
silicon nitride (SiN), tungsten (W), titanium tungsten (TiW), or
copper (Cu); and the bottom electrode 402 is formed from a metal,
such as W, Cu, Aluminum (Al), or molybdenum (Mo). Also, in various
examples: the electro-active materials 406A and 406B are formed
from aluminum nitride (AlN) or lead zirconate titanate (PZT); the
insulative layers 412A and 412B are formed from an oxide material;
the top electrodes 404A and 404B are formed from a metal, such as
W, Cu, Al or Mo; and the electro-active materials 408A and 408B
include layers from different materials, such as SiC, MSQ, SiO2,
SiCOH, SiN, W, TiW or Cu.
In operation, the three-electrode BAW resonator core 400 has two
active area 415A and 415B, where mechanical energy is confined and
isolated. The active areas 415A and 415B are created by the various
layers and applied signals. More specifically, the active area 415A
occurs where overlap exists between the bottom electrode 402 and
the top electrode 404A. Also, the active area 415B occurs where
overlap exists between the bottom electrode 402 and the top
electrode 404B. As shown, some of the layers used to create the
active areas 415A and 415B are shared (e.g., the substrate 401, the
electro-active materials 410, and the bottom electrode 402), while
other layers are separated and are on opposite sides of the metal
node 430 (e.g., mirrored from line 420). More specifically, the
electro-active materials 406A, the top electrode 404A, and the
electro-active materials 408A, are arranged to the left side of the
metal node 430 and contribute to the active area 415A. Meanwhile,
the electro-active materials 406B, the top electrode 404B, and the
electro-active materials 408B, are arranged to the right side of
the metal node 430, and contribute to the active area 415B. When a
DC tuning voltage is applied (via the metal node 430 and the bottom
electrode 402, the behavior of the active areas 415A and 415B is
modified due to the effect of the DC voltage on a physical
characteristic (e.g., size, internal stress/strain, and/or shape)
of one or more of the electro-active materials 410, 406A, 406B,
408A, and 408B, such that the center frequency of the
three-electrode BAW resonator core 400 is shifted.
FIG. 5 shows a cross-sectional view of a pair of two-electrode BAW
resonator cores 500 and 530 used for a tunable BAW resonator device
in accordance with various examples (such as FIGS. 1B and 1C). Each
of two-electrode BAW resonator cores 500 and 530 in FIG. 5 is an
example of an SMR that includes various layers formed over
respective semiconductor substrates 501 and 531. As shown in FIG.
5, the two-electrode BAW resonator core 500 includes various layers
formed over a semiconductor substrate 501. More specifically, the
layers formed over the semiconductor substrate 501 include
electro-active materials 510 (e.g., Bragg mirrors), a bottom
electrode 502, electro-active materials 506 (e.g., piezoelectric
materials), an insulative layer 512, a top electrode 504, and
electro-active materials 508 (e.g., Bragg mirrors). The
two-electrode BAW resonator core 500 also includes a first metal
node 520 coupled to the top electrode 504, and a second metal node
522 coupled to the bottom electrode 502. In some examples, the
metal node 520 is oscillator terminal 123 (of the device 120 in
FIG. 1B) or oscillator terminal 143 (of the device 140 in FIG. 1C).
In other examples, the metal node 520 is coupled to an external
metal terminal (not shown) that facilitates coupling a tunable BAW
device with the pair of two-electrode BAW resonator cores 500 and
530 to other components (e.g., components of an oscillator unit, a
clock unit, or an IC unit). Also, in some examples, the second
metal node 522 is coupled to an external metal terminal (not
shown), which is the DC tuning terminal 127 (of the device 120 in
FIG. 1B) or the DC tuning terminal 147 (of the device 140 in FIG.
1C).
The second two-electrode BAW resonator core 530 also includes
various layers formed over a semiconductor substrate 531. More
specifically, the layers formed over the semiconductor substrate
531 include electro-active materials 540 (e.g., Bragg mirrors), a
bottom electrode 532, electro-active materials 536 (e.g.,
piezoelectric materials), an insulative layer 542, a top electrode
534, and electro-active materials 538 (e.g., Bragg mirrors). The
two-electrode BAW resonator core 530 also includes a first metal
node 550 coupled to the top electrode 534, and a second metal node
552 coupled to the bottom electrode 532. In some examples, the
first metal node 550 is oscillator terminal 125 (of the device 120
in FIG. 1B) or oscillator terminal 145 (of the device 140 in FIG.
1C). In other examples, the first metal node 550 is coupled to an
external metal terminal (not shown) that facilitates coupling a
tunable BAW device with the pair of two-electrode BAW resonator
cores 500 and 530 to other components (e.g., components of an
oscillator unit, a clock unit, or an IC unit). Also, in some
examples, the second metal node 552 is coupled to an external metal
terminal (not shown), which is the DC tuning terminal 127 (of the
device 120 in FIG. 1B) or the DC tuning terminal 147 (of the device
140 in FIG. 1C). In the above description, the top electrodes 504
and 534 are coupled to separate oscillator terminals, while the
bottom electrodes 502 and 532 are coupled to a DC turning terminal.
In other examples, the top electrodes 504 and 534 are coupled to a
DC tuning terminal, while the bottom electrodes 502 and 532 are
coupled to separate oscillator terminals.
In various examples: the substrates 501 and 531 are formed from
silicon; the electro-active materials 510 and 540 include layers
from different materials, such as SiC, MSQ, SiO2, SiCOH, SiN, W,
TiW or Cu; and the bottom electrodes 502 and 532 are formed from a
metal, such as W, Cu, Al or Mo. Also, in various examples: the
electro-active materials 506 and 536 are formed from AlN or PZT;
the insulative layers 512 and 542 are formed from oxide materials;
the top electrodes 504 and 534 are formed from a metal, such as W,
Cu, Al or Mo; and the electro-active materials 508 and 538 include
layers from different materials, such as SiC, MSQ, SiO2, SiCOH,
SiN, W, TiW or Cu.
In operation, the pair of two-electrode BAW resonator cores 500 and
530 have two active area 515 and 545, where mechanical energy is
confined and isolated. The active areas 515 and 545 are created by
the various layers and applied signals. More specifically, the
active area 515 occurs where overlap exists between the bottom
electrode 502 and the top electrode 504 in the two-electrode BAW
resonator core 500. Meanwhile, the active area 545 occurs where
overlap exists between the bottom electrode 532 and the top
electrode 534 in the two-electrode BAW resonator core 530. When a
DC tuning voltage is applied (passed to the metal nodes 522 and 552
and then the bottom electrodes 502 and 532), the behavior of the
active areas 515 and 545 is modified due to the effect of the DC
voltage on a physical characteristic (e.g., size, internal
stress/strain, and/or shape) of one or more of the electro-active
materials 510, 540, 506, 536, 508 and 538, such that the center
frequency of each two-electrode BAW resonator core 500 and 530 is
shifted.
In various examples, the tunable BAW resonator devices described
herein are formed using SMR cores (e.g., the cores 400, 500, and
530 in FIGS. 4 and 5). In other examples, the tunable BAW resonator
devices described herein are formed using film bulk acoustic
resonator (FBAR) cores. FBARs are mechanical resonators formed from
electro-active materials (e.g., piezoelectric materials) sandwiched
between two metal electrodes. The main difference between FBAR and
SMR is that FBARs employ a "released" structure, such that the
electro-active materials and electrodes are freely suspended in
space, with the help of some support beams or layers. FBARs have
free boundary conditions at the outer surfaces of the electrodes as
opposed to SMRs where the electrodes are part of a solid structure
without air gaps.
FIGS. 6A-6C show block diagrams of BAW resonator cores and related
terminals in accordance with various examples. In FIG. 6A, certain
layers of a three-electrode BAW resonator core 600 are represented
(e.g., example layers of the three-electrode BAW resonator core 400
of FIG. 4). As shown, the represented layers include a set of
acoustic mirror layers 618 that alternate between dielectric or
ferroelectric layers 620 and 624, and acoustic mirror metal layers
622 and 626. In different examples, the number of layers in the set
of acoustic mirror layers 618 varies. A bottom electrode 602 is
formed above the set of acoustic mirror layers 618. Above the
bottom electrode 602, separate piezoelectric layers 616 and 606 are
formed. Finally, top electrodes 614 and 604 are formed above
respective piezoelectric layers 616 and 606.
With the three-electrode BAW resonator core 600 represented in FIG.
6A, the top electrode 614 is coupled to an oscillator terminal 613
(e.g., to receive a differential AC signal, V+), and the other top
electrode 604 is coupled to another oscillator terminal 615 (e.g.,
to receive a differential AC signal, V-). The bottom electrode 602
is coupled to a DC tuning terminal 617 (e.g., to receive a DC
tuning signal, Vtune). In another example, the DC tuning terminal
617 is coupled to one of the acoustic mirror metal layers 622 or
626, instead of (or in addition to) the bottom electrode 602. Also,
in some examples, the differential AC signal received by each of
the top electrodes 604 and 614 is switched so that top electrode
614 receives the differential AC signal V- instead of V+, and top
electrode 604 receives the differential AC signal V+ instead of V-.
When Vtune is applied, the center frequency for the three-electrode
BAW resonator core 600 is shifted.
In some examples, a pair of two-electrode BAW resonator cores
(e.g., cores 500 and 530 in FIG. 5) are used together, instead of a
three-electrode BAW resonator core. This scenario can be seen by
removing section 628 of the three-electrode BAW resonator core 600.
In such examples, a DC tuning terminal (e.g., terminal 617) is
coupled to a bottom electrode and/or to an acoustic mirror metal
layer for each two-electrode BAW resonator core. Meanwhile, the top
electrodes of each two-electrode BAW resonator core are coupled to
different oscillator terminals (e.g., one to V+ and the other to
V-). When Vtune is applied, the center frequency for each
two-electrode BAW resonator core is shifted.
In FIG. 6B, certain layers of a two-electrode BAW resonator core
630 are represented (e.g., example layers for either of the
two-electrode BAW resonator cores 500 and 530 of FIG. 5). As shown,
the represented layers include a set of acoustic mirror layers 638
that alternate between dielectric or ferroelectric layers 640 and
644, and acoustic mirror metal layers 642 and 646. In different
examples, the number of layers in the set of acoustic mirror layers
638 varies. A bottom electrode 632 is formed above the set of
acoustic mirror layers 638. Above the bottom electrode 632, a
piezoelectric layer 636 is formed. Finally, a top electrode 634 is
formed above the piezoelectric layer 636.
With the two-electrode BAW resonator core 630 represented in FIG.
6B, the top electrode 634 is coupled to an oscillator terminal 643
(e.g., to receive a differential AC signal, V+), and the bottom
electrode 632 is coupled to another oscillator terminal 645 (e.g.,
to receive a differential AC signal, V-). The top electrode 634
also is coupled to a DC tuning terminal 647 (e.g., to receive a DC
tuning signal, Vtune). As desired, an isolator is positioned
between the oscillator terminal 643 and the DC tuning terminal 647
to prevent the DC tuning signal from being passed to oscillator
core components (such as in FIGS. 1A and 3A). In some other
examples, the electrodes 632 and 634 are coupled to different
oscillator terminals (e.g., electrode 632 to a V+ terminal and
electrode 634 to a V+ terminal). When Vtune is applied, the center
frequency for the two-electrode BAW resonator core 630 is
shifted.
In FIG. 6C, certain layers of a two-electrode BAW resonator core
650 are represented (e.g., example layers for either of the
two-electrode BAW resonator cores 500 and 530 of FIG. 5). As shown,
the represented layers include a set of acoustic mirror layers 670
that alternate between dielectric or ferroelectric layers 672 and
676, and acoustic mirror metal layers 674 and 678. In different
examples, the number of layers in the set of acoustic mirror layers
670 varies. A bottom electrode 652 is formed above the set of
acoustic mirror layers 670. Above the bottom electrode 652, a
piezoelectric layer 656 is formed. Finally, a top electrode 654 is
formed above the piezoelectric layer 656.
With the two-electrode BAW resonator core 650 represented in FIG.
6C, the top electrode 654 is coupled to an oscillator terminal 663
(e.g., to receive a differential signal, V+), and the bottom
electrode 652 is coupled to another oscillator terminal 665 (e.g.,
to receive a differential signal, V-). Meanwhile, a DC tuning
terminal 667 is coupled to the acoustic mirror metal 674 of the
two-electrode BAW resonator core 650. When Vtune is applied, a
static mechanical stress along with mechanical strain are induced
in the mirror stack (either by electrostatic attraction or by
piezoelectric effect if layer 672 is ferroelectric. The static
stress is coupled to the entire structure, which causes the center
frequency for the two-electrode BAW resonator core 650 to be
shifted.
FIG. 7 shows a graph 700 representing BAW resonator frequency shift
as a function of a DC tuning voltage in accordance with test
results. As shown in graph 700, adjusting a DC tuning voltage by 2
volts adjusts a center frequency for each of multiple BAW
resonators by approximately 50 ppm in a linear manner. The linear
relationship between the DC tuning voltage and center frequency
shifts means tunable BAW resonator devices should have an expected
range of frequency shift for a given DC tuning signal range. Thus,
tunable BAW resonator devices and related units can be made to
support a desired amount of frequency shift capability.
FIG. 8 shows a graph 800 representing BAW resonator quality factor
(Q) as a function of a DC tuning voltage in accordance with test
results. As shown in graph 800, adjusting a DC tuning voltage does
not significantly affect a quality factor for each of multiple BAW
resonators. Accordingly, the quality factor of tunable BAW
resonator devices should not be significantly affected by DC
tuning. Thus, each tunable BAW resonator devices described herein
is expected to perform similar to a two-terminal BAW resonator
device (high-impedance except at a narrow frequency range). This is
an improvement over existing BAW resonator tuning schemes (e.g.,
coupling a capacitor across each terminal of a two-terminal BAW
resonator device) that cause significant degradation in quality
factor and impedance at resonance. This ultimately leads to higher
phase noise and power consumption.
FIG. 9 shows a flowchart of a tunable BAW resonator device
fabrication method 900 in accordance with various examples. As
shown, the method 900 comprises forming a shared bottom electrode
at block 902. At block 904, separate piezoelectric layers are
formed on the shared bottom electrode. At block 906, top electrodes
are formed on each piezoelectric layer. For example, the method 900
is used when fabricating a tunable BAW resonator device that
includes a three-electrode BAW resonator core (such as device 160
of FIG. 1D, and the three-electrode BAW resonator core 400 of FIG.
4).
FIG. 10 shows a flowchart of another tunable BAW resonator device
fabrication method 1000 in accordance with various examples. As
shown, the method 1000 comprises obtaining a two-electrode BAW
resonator core at block 1002. The two-electrode BAW resonator core
of block 1002 can be manufactured or purchased from a supplier. At
block 1004, an isolator (e.g., a capacitor or another isolation
component) is added between each electrode and a respective
oscillator terminal. At block 1006, a DC tuning terminal is
connected to a point (such as the connection point 116 in FIG. 1A)
between an isolator and an electrode of the two-electrode BAW
resonator core. In various examples, the method 1000 includes
additional steps, such as coupling a resistor between the DC tuning
terminal and the connection point of block 1006 (such as resistor
108 in FIG. 1A). Also, another resistor (such as resistor 109 in
FIG. 1A) can be added between ground and a connection point (such
as the connection point 118 in FIG. 1A) between the other electrode
and isolator. For example, the method 1000 is used when fabricating
a tunable BAW resonator device that includes a single two-electrode
BAW resonator core (such as device 100 of FIG. 1D).
FIG. 11 shows a flowchart of a tunable BAW resonator device
fabrication method 1100 in accordance with various examples. As
shown, the method 1100 comprises forming a first two-electrode BAW
resonator core at block 1102 (e.g., the two-electrode BAW resonator
core 500 of FIG. 5). At block 1104, a second two-electrode BAW
resonator core (e.g., the two-electrode BAW resonator core 530 of
FIG. 5) is formed. At block 1106, a first electrode of the first
two-electrode BAW resonator core is coupled to a first oscillator
terminal (e.g., the top electrode 504 of the two-electrode BAW
resonator core 500 in FIG. 5 is coupled to metal node 520 or an
external oscillator terminal). At block 1108, a first electrode of
the second two-electrode BAW resonator core is coupled to a second
oscillator terminal (e.g., the top electrode 534 of the
two-electrode BAW resonator core 530 in FIG. 5 is coupled to metal
node 550 or an external oscillator terminal). At block 1110,
respective second electrodes of the first and second two-electrode
BAW resonator cores are coupled to a DC tuning terminal (e.g., the
bottom electrodes 502 and 532 of the two-electrode BAW resonator
cores 500 and 530 in FIG. 5 are coupled to metal nodes 522 and 552,
each coupling to an external DC tuning terminal). For example, the
method 1100 is used when fabricating a tunable BAW resonator device
that includes a pair of two-electrode BAW resonator cores (such as
device 120 or 140 of FIGS. 1B and 1C). Also, method 1100 can be
combined with method 900, where performing blocks 1102 and 1104 in
method 1100 involves performing blocks 902, 904, and 906 in method
900. Also, in various examples, the steps represented in methods
900, 1000, and 1100 are performed in a different order and/or are
performed simultaneously.
FIG. 12 shows a flowchart of a method 1200 involving a tunable BAW
resonator device in accordance with various examples. As shown, the
method 1200 comprises providing a tunable BAW resonator device at
block 1202. At block 1204, a DC tuning controller is provided for
the tunable BAW resonator device. At block 1206, an oscillator
circuit is provided. At block 1208, a DC tuning signal applied to
the tunable BAW resonator device is selectively adjusted by the DC
tuning controller to adjust a signal frequency of the oscillator
circuit.
In some examples of the method 1200, the tunable BAW resonator
device comprises a single two-electrode BAW resonator core, and the
method 1200 further comprises coupling the single two-electrode BAW
resonator core to the DC tuning controller and the oscillator
circuit via isolated terminals. In some examples of the method
1200, the tunable BAW resonator device comprises a pair of
two-electrode BAW resonator cores, and the method 1200 further
comprises coupling the pair of two-electrode BAW resonator cores to
the DC tuning controller and the oscillator circuit via isolated
terminals. In some examples of the method 1200, the tunable BAW
resonator device comprises a single three-electrode BAW resonator
core, and the method 1200 further comprises coupling the single
three-electrode BAW resonator core to the DC tuning controller and
the oscillator circuit via isolated terminals. In some examples,
the method 1200 also comprises: receiving, by the DC tuning
controller, an ambient measurement (e.g., a temperature and/or
stress measurement); and adjusting the DC tuning signal applied to
the tunable BAW resonator device based on the ambient measurement.
In some examples, the method 1200 also comprises: receiving, by the
DC tuning controller, a drift frequency measurement or estimate;
and adjusting the DC tuning signal applied to the tunable BAW
resonator device based on the drift frequency measurement or
estimate.
In this description, the term "couple" or "couples" means either an
indirect or direct wired or wireless connection. Thus, if a first
device is coupled to a second device, that connection may be
through a direct connection or through an indirect connection via
other devices and connections. Also, in this description, the
recitation "based on" means "based at least in part on." Therefore,
if X is based on Y, then X may be a function of Y and any number of
other factors.
Modifications are possible in the described embodiments, and other
embodiments are possible, within the scope of the claims.
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